Power converters such as, for example, converters embodying flyback topologies, are subject to safety considerations requiring limits on the maximum output power over a wide range of inputs. Although such converters utilize a current mode controller to limit the peak current of the primary switch of the flyback converter transformer, the output power can still vary to undesirable levels over large input line variations. Previous approaches to control output power have included operating the converter in a discontinuous mode, or the use of a latch-off or hiccup mode of operation when excessive output power is detected. The discontinuous mode technique requires significantly higher primary peak currents to provide full output power. The latch-off or hiccup mode requires extra power/current sensing and control circuits, increasing the complexity and cost of such power control circuits.
A need has thus arisen for a low cost limiting output power control circuit for a flyback converter.